1. Field of the Invention
This invention relates to the art of detecting water leaks, and more particularly, to an improved apparatus for localizing underground waer leakages. The invention is specifically concerned with a listening device which is incorporated in a test rod for sensing water leakage noises.
2. Description of the Prior Art
It is well known in the water leakage detection art to employ manual listening boxes and mechanical geophones. It is also known in the prior art to employ electro-acoustic listening devices which employ sensitive microphones. A detailed discussion of the last mentioned prior art water leak detecting apparatuses may be found in U.S. Pat. No. 3,458,656. Other examples of apparatuses for detecting leaks in underground water systems are shown in U.S. Pat. Nos. 1,830,237; 2,755,336; 2,755,880; 2,900,039; 3,223,194, and 3,264,864. It is also known in the water leak detecting art to employ a test rod pick-up of the magnetic variable reluctance type, which employs a diaphragm mounted in a cavity. A magnetic variable reluctance type water leakage detector is available on the market from Health Consultants Incorporated, 100 Tosca Drive, Stoughton, Massachusetts 02072, under the trademark "SON-I-KIT", test rod pick-up. When sound reaches the cavity, the diaphragm vibrates and varies a magnetic field density to induce an alternating current in a pick-up coil which is connected to a suitable amplifier-receiver and heatset. A disadvantage of the last mentioned variable reluctance pick-up testing rod is that it is costly, and it will not withstand high impacts which cause fractures in the apparatus, and it is not waterproof. The magnetic variable reluctance pick-up is also subject to magnetic fields which often create problems in using this type of pick-up.